1. Technical Field of the Invention
The present invention relates to telecommunications equipment and, more particularly, to a system and method for recovering a communications node with a redundant matrix architecture upon detecting a failure before the network (e.g., a Signaling System No. 7 (SS7) network) in which the node is disposed attempts to take down the communications link between the node and the network.
2. Description of Related Art
Out-of-band signaling establishes a separate channel for the exchange of signaling information between call component nodes in order to set up, maintain and service a call in a telephony network. Such channels, called signaling links, are used to carry all the necessary signaling messages between the nodes. Thus, for example, when a call is placed, the dialed digits, trunk selected, and other pertinent information are sent between network switches using their signaling links, rather than the trunks which will ultimately carry the bearer traffic, i.e., conversation.
Out-of-band signaling has several advantages that make it more desirable than traditional in-band signaling. First, it allows for the transport of more data at higher speeds than multi-frequency (MF) outpulsing used in the telephony networks without SS7. Also, because of separate trunks and links, signaling can be done at any time in the entire duration of the call, not just at the beginning. Furthermore, out-of-band signaling enables signaling to network elements to which there is no direct trunk connection.
SS7 packet signaling has become the out-of-band signaling scheme of choice between telephony networks and between network elements worldwide. Three essential components are defined in a signaling network based on SS7 architecture. Signal Switching Points (SSPs) are basically telephone switches equipped with SS7 -capable software that terminate signaling links. SSPs generally originate, terminate, or switch calls. Signal Transfer Points (STPs) are the packet switches of the SS7 network. In addition to certain specialized functions, they receive and route incoming signaling messages towards their proper destination. Finally, Signal Control Points (SCPs) are databases that provide information necessary for advanced call-processing and Service Logic execution.
As is well known, SS7 signaling architecture is governed by several multi-layered protocols standardized under the American National Standards Institute (ANSI) and the International Telecommunications Union (ITU) to operate as the common xe2x80x9cgluexe2x80x9d that binds the ubiquitous autonomous networks together so as to provide a xe2x80x9cone networkxe2x80x9d feel that telephone subscribers have come to expect.
The exponential increase in the number of local telephone lines, mobile subscribers, pages, fax machines, and other data devices, e.g., computers, Information Appliances, etc., coupled with deregulation that is occurring worldwide today is driving demand for small form factor, high capacity STPs which must be easy to maintain, provide full SS7 functionality with so-called xe2x80x9cfive ninesxe2x80x9d operational availability (i.e., 99.999% uptime), and provide the capability to support future functionality or features as the need arises. Further, as the subscriber demand for more service options proliferates, an evolution is taking place to integrate Intelligent Network (IN)-capable SCP functionality within STP nodes.
Those skilled in the art should readily recognize that several difficulties must be overcome in order to integrate the requisite functionalities into a suitable network element that satisfies the stringent performance criteria, e.g., high degree of operational availability, required of telecommunications equipment. Challenges arise in designing a compact enough form factor that is efficiently scalable, ruggedized, and modularized for easy maintenance, yet must house complex electronic circuitry, e.g., processors, control components, timing modules, I/O, line interface cards which couple to telephony networks, that is typically required for achieving the necessary network element functionality. In addition, such complexity in the equipment increases the probability of various single point failures that cause downtime. These failures can be caused by a variety of errors in timing and data paths (e.g., framing errors, loss of signal, loss of alignment, etc.), mechanical problems, electronic component and board failures, and loss of device communication, e.g., cabling problems.
It is well known that redundant architectures are utilized in designing telecommunications equipment in order to minimize the risk of such failures as described hereinabove. Most, if not all, of the switching hardware of a network element (i.e., a telecommunications node) is provided in a duplexed or redundant matrix configuration wherein the devices (and the data and timing paths effectuated thereby) are organized into two planes or sides which are mirror images of each other. One of the planes operates as the master plane that carries valid data and timing for the node, whereas the other plane is provided as a standby. Consequently, when a failure is encountered on the master side during the operation of the equipment, the standby side becomes active and the matrix accordingly switches to that side.
Although advances such as redundancy are effective in increasing network element availability, current solutions for providing redundancy in telecommunications equipment are beset with several deficiencies and shortcomings. For example, one of the more serious consequences of the existing redundancy architectures which are provided as cross-coupled matrix planes is that the time for detecting a failure and effectuating a switchover accordingly is too long compared to the reaction time of the network. For instance, the reaction time for SS7 networks to fail a link is between 48 and 128 milliseconds (depending on the data patterns received). Accordingly, if the failure detection and switchover are not completed by the node within that time window, the SS7 link between the node and the network will be taken down by the network (i.e., the switch provided on the other side of the link).

Accordingly, the present invention is directed in one aspect to a communications node disposed in a telecommunications network that maintains its communications link by rapidly switching planes before the link is taken down by the network when a failure is encountered in the node. The communications node comprises a redundant matrix that is organized in a planar mode having a first side and a second side, wherein data and timing paths of the first side are de-coupled from the data and timing paths of the second side. There is at least one trunk-interfacing end device for interfacing with the telecommunications network via a communications link. The trunk-interfacing end devices are coupled to the redundant matrix at a first terminus. At a second terminus, one or more channel-controller end devices are coupled to the redundant matrix. That is, the trunk-interfacing end devices (circuits/channels) and channel-controller end devices (channels/circuits/links) are connected to each other through the redundant matrix. The communications node is provided with a plurality of end-to-end test channels used for monitoring a failure condition associated with the redundant matrix. Hardware, firmware, and software modules are provided for switching the operation of the communications node from the active side to the standby side when a failure is detected in the active side, the switchover being effectuated within a time window that permits continued maintenance of the link.
In another aspect, the present invention relates to a link maintenance method for use in a communications node disposed in a telecommunications network, wherein the communications node is organized as a de-coupled redundant matrix having a first side and a second side. The communications node is placed and operated in a planar mode such that revenue traffic between the communications node and the telecommunications network traverses either the first side or the second side of the redundant matrix. The side carrying the revenue traffic is designated as the master side, the other side being the standby side. In the planar mode of operation, the data and timing paths of the first side are completely de-coupled from the data and timing paths of the second side such that single point failures are easily isolated in the matrix to one side or the other. The master side of the redundant switching matrix is monitored for a failure condition associated therewith by employing a plurality of test channels in the redundant matrix. At least one predetermined or fixed test pattern is preferably continuously propagated on the dedicated (i.e., xe2x80x9cnailed upxe2x80x9d) test channels for detecting any variances therein by monitors enabled in the trunk-interfacing end devices of the node. The operation of the communications node is switched from the side with a failure to the other side with good timing and data, provided auto-switchover is enabled. Preferably, auto-switchover is enabled when all the matrix devices of both matrix planes are in-service, i.e., capable of handling SS7 traffic. In a presently preferred exemplary embodiment, when a failure condition is detected, the communications node injects appropriate idle codes towards the network such that the link is placed in a xe2x80x9choldxe2x80x9d mode. The link is thereby prevented from being taken down by the network. Upon the switchover, the idle codes are turned off so that the link is operational for transporting signal traffic again.
In yet further aspect, the present invention is directed to a signaling node (e.g., an STP) disposed in a Signaling System No. 7 (SS7 ) network for switching between a plurality of SS7 links. The signaling node comprises a planar redundant matrix with a master side and a standby side wherein revenue traffic between the signaling node and the SS7 network runs on the master side encoded in pulse code modulation (PCM) form. In the planar mode of operation, data and timing paths of the master s de are de-coupled from the data and timing paths of the standby side. A plurality of Digital Trunk Interface (DTI) devices are disposed on a first terminus of the planar redundant matrix for interfacing with the SS7 network, wherein each DTI device supports two E1 spans (each with 30 revenue channels and two test channels). A plurality of bus terminator devices (BTDs) are coupled to the DTI devices for providing appropriate timing for the DTI devices. Preferably, one BTD device is capable of serving up to six DTI devices. A plurality of DS1 Channel Controller (DCC) devices are disposed on a second terminus of the planar redundant matrix for managing appropriate protocol conversion between the PCM revenue traffic and SS7 messages. Firmware monitors are provided in the DTI devices that detect failure conditions in the master side by monitoring for variance(s) in fixed test patterns injected into matrix test channel connections. Preferably, errors in PCM data, timing, and errors relating to device communication are detected by the firmware monitors when a test pattern variance is observed. Hardware, firmware, and software components are provided in a distributed architecture in the node for switching the data/timing paths for the DTI and DCC devices from the master side to the standby side of the planar matrix when a failure condition is encountered in the master side.